The proposed objectives are: To ascertain whether classical immunological tolerance to avian oncornavirus antigens and virus-induced surface antigens exists at the humoral or cellular levels; to determine the specificity of this tolerance; To isolate virus-induced surface antigen and to study its role in the evocation and operation of immunity to avian oncornaviruses. BIBLIOGRAPHIC REFERENCE: Meyers, P. Antibody Response to Related Leukosis Viruses in Chickens Tolerant to an Avian Leukosis Virus. J. Natl. Cancer Inst. 56 381-386, 1976. Meyers, P. and L.F. Qualtiere. The Efficacy of Chemical Bursectomy in Chickens with Congenital Leukosis Virus Infection. Immunol. 31 527-532, 1976.